Several types of thermoset polymers are generally used in commerce. One type is the acrylic thermoset polymers cured by a free radical addition mechanism. These polymers are cured by heat initiators, such as peroxides, or by photoinitiators, such as alpha diketones. A characteristic of the cured acrylates, however, is large polymerization shrinkage, which is undesirable for many uses. Another undesirable characteristic of acrylates is the formation of an oxygen-inhibited layer on the surface upon curing.
Another type of thermoset polymers is the one based on cationic polymerization of oxirane (epoxy) monomers. These are cured by use of a two-part system or by use of photoinitiators. The disadvantages of oxirane-derived polymers, however, are high water uptake in service, large polymerization shrinkage, and high cost.
Another type of thermoset polymers is the one based on a ring-opening metathesis polymerization (ROMP) mechanism. Metathesis is generally understood to mean the metal catalyzed redistribution of carbon-carbon double bonds. The polymerizable composition comprises a resin system that includes functionalities or groups that are curable by ROMP together with a metathesis catalyst, such as a ruthenium carbene complex. In addition to ROMP, other metathesis reaction systems utilize metathesis catalysts, for example ring closing metathesis, acyclic diene metathesis polymerization, ring opening metathesis and cross metathesis.
The thermoset monomer types that are curable by ROMP are the cycloolefins, such as dicyclopentadiene (DCPD), as described in Woodson U.S. Pat. No. 6,310,121. Various other patents address the polymerization of cyclic olefins such as DCPD, tricyclododecene and the like, for example, Tom U.S. Pat. No. 4,584,425. Two of these patents mention compounds containing norbornenyl functional groups and ROMP with the goal of producing a highly crosslinked polymer, namely Bissinger U.S. Pat. No. 6,075,068 and EP 1025830A2 by Moszner. Bissinger describes several ROMP catalyzed resin systems based on dinorbornenyl dicarboxylate ester (DNBDE) compounds or a combination of DNBDE compounds and acrylates. A trinorbornenyl tricarboxylate ester (TNBTE) compound was also disclosed. Moszner describes ROMP of norbornenyl monocarboxylate, which is a monofunctional monomer. However, the combination of the particular resins and catalysts does not achieve the controlled reaction progress desired for many applications.
In dentistry, addition silicones are the most widely used impression materials. Addition silicones cure with a hydrosilation mechanism and contain a platinum compound as a catalyst. Despite the addition of various surfactants, the hydrophilicity of the materials as measured by contact angle measurements, especially before set is completed, is very low. This reduces the ability of the impression material to displace oral fluids during curing and results in a compromised impression. Another class of impression material, the polyethers, as exemplified by IMPREGUM® (from 3M ESPE) are 2-part systems containing imine terminated polyether copolymers cured by reaction with a strong acid. However, these polyethers suffer from high rigidity, which is a property of crosslinked polyethers, and poor taste and smell due to the presence of imines and strong acids.
There is thus a need for a polyether-based impression material with improved flexibility, taste and smell.